In an automated manufacturing setting, actuators perform basically two functions. Actuators are used to move work and to apply useful force to the work. Sometimes it may be desirable to combine both of these functions in a single actuator. As an example in the manufacture of a part, it may be necessary to move a cutting tool into position with respect to the part and then to apply some force to the cutting tool to shape the part. In the assembly of a multi component part, it may be necessary to precisely locate or position a part in the assembly and then apply a known force to the part in order to perform an operation of the assembly procedure.
In general a useful goal in the design of any automated manufacturing equipment is to engineer the simplest lowest cost system that will successfully perform the work. Prior to 1975 machine tools moved cutting tools in and out of position using hydraulic servo valves. Such servo valves enable the system to be designed to achieve multiple precise positioning at varying speeds. The advent of inexpensive computer controls led to the almost complete replacement of such devices with electric servo and stepper devices. Hydraulic devices are now primarily used in high force applications.
In automated assembly or automated inspection of parts, components of the system must meet multiple requirements. Among these requirements are precision movement and precise positioning of parts and feedback that a movement of the part was successful. These requirements are even more difficult with small or lightweight parts. An assembly may sometimes also require the application of a large force upon the part at the end of the movement.
Electrical devices are good for fast and precise variable movement. Electrical devices also provide good position feedback. On the other hand, electrical devices must be relatively large to exert substantial forces. A drawback of large electrical devices is that inertia limits the speed of a large device. This slows down the speed of the operation. In addition large electrical devices consume a large quantity of electricity.
The present invention recognizes that pneumatic devices can complement electrical devices in accomplishing this type of work in automated applications. Air devices can supply large forces in a small lightweight package. Air cylinders, however, can not be variably moved and precisely positioned because variable sensing is lacking and air is a compressible fluid. A combination of an air and electric device, however, can be used to achieve both objectives.
The present invention utilizes small high speed electric devices such as the electric actuators disclosed in the above cited parent application in combination with a pneumatic actuator. With such a combined system the electric actuator can be used to precisely position or locate the work and the pneumatic actuator to apply a known force to the work. In this application, the electric actuator provides precision movement and the pneumatic actuator provides a desired force. In an alternate embodiment of the invention, a pneumatic actuator can be used to move the work through a relatively large distance (dumb movement) and an electric actuator as disclosed in the above cited parent application, can be used to precisely and variably position (i.e. precise movement) the work prior to or following the large movement.
Accordingly it is an object of the present invention to provide an actuator for precisely moving or contacting a part and then for applying a relatively large force to the part. It is another object of the present invention to provide an electric/pneumatic actuator in which a part can be precisely and variably positioned or contacted using an electric actuator and then a force can be applied to the part using a pneumatic actuator. Still another object of the present invention is to provide a pneumatic/electric actuator in which a relatively large movement can be achieved using a pneumatic actuator or the like and the large movement precisely and variably controlled at either end of the large movement with an electric actuator. Yet another object of the present invention is to provide an pneumatic/electric actuator that is compact and relatively inexpensive to manufacture and use.